The proposed project will identify patients with glycogen storage disease by enzyme assays in blood cells, cultured skin fibroblasts, serum and urine. Only if necessary will enzyme assays in biopsy material be used. Once the patients are identified, we will study the pattern of inheritance in their family and try to identify carriers. Genetic variation will be studied as well as properties of the residual enzyme activity present in some of the cases of glycogen storage diseases. Some lysosomal storage diseases will also be studied.